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<div class="title">randomizedselect.h</div>  </div>
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<a href="randomizedselect_8h.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno">    1</span>&#160;<span class="preprocessor">#ifndef RANDOMIZED_SELECT</span></div>
<div class="line"><a name="l00002"></a><span class="lineno">    2</span>&#160;<span class="preprocessor">#define RANDOMIZED_SELECT</span></div>
<div class="line"><a name="l00003"></a><span class="lineno">    3</span>&#160;<span class="preprocessor">#include&lt;<a class="code" href="quicksort_8h.html">src/sort_algorithms/quick_sort/quicksort.h</a>&gt;</span></div>
<div class="line"><a name="l00004"></a><span class="lineno">    4</span>&#160;<span class="preprocessor">#include &lt;random&gt;</span></div>
<div class="line"><a name="l00005"></a><span class="lineno">    5</span>&#160;<span class="keyword">namespace </span><a class="code" href="namespace_introduction_to_algorithm.html">IntroductionToAlgorithm</a></div>
<div class="line"><a name="l00006"></a><span class="lineno">    6</span>&#160;{</div>
<div class="line"><a name="l00007"></a><span class="lineno">    7</span>&#160;    <span class="keyword">namespace </span>SelectAlgorithm</div>
<div class="line"><a name="l00008"></a><span class="lineno">    8</span>&#160;    {</div>
<div class="line"><a name="l00009"></a><span class="lineno">    9</span>&#160;</div>
<div class="line"><a name="l00011"></a><span class="lineno">   11</span>&#160;</div>
<div class="line"><a name="l00018"></a><span class="lineno"><a class="line" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#a117ee8d5d70d91c5be1d412f9fbad1cd">   18</a></span>&#160;     <span class="keyword">template</span>&lt;<span class="keyword">typename</span> IntType&gt; IntType  <a class="code" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#a117ee8d5d70d91c5be1d412f9fbad1cd">radom_index</a>(IntType begin,IntType end)</div>
<div class="line"><a name="l00019"></a><span class="lineno">   19</span>&#160;     {</div>
<div class="line"><a name="l00020"></a><span class="lineno">   20</span>&#160;         assert(end&gt;=begin);</div>
<div class="line"><a name="l00021"></a><span class="lineno">   21</span>&#160;         <span class="keyword">static</span> std::random_device rd; <span class="comment">//每一个std::random_device维持相同的伪随机序列，因此需要用静态变量保证只有一个std::random_device</span></div>
<div class="line"><a name="l00022"></a><span class="lineno">   22</span>&#160;         std::mt19937 gen(rd());</div>
<div class="line"><a name="l00023"></a><span class="lineno">   23</span>&#160;         std::uniform_int_distribution&lt;IntType&gt; dis(begin, end);</div>
<div class="line"><a name="l00024"></a><span class="lineno">   24</span>&#160;         <span class="keywordflow">return</span> dis(gen);</div>
<div class="line"><a name="l00025"></a><span class="lineno">   25</span>&#160;     }</div>
<div class="line"><a name="l00026"></a><span class="lineno">   26</span>&#160;</div>
<div class="line"><a name="l00028"></a><span class="lineno">   28</span>&#160;</div>
<div class="line"><a name="l00045"></a><span class="lineno">   45</span>&#160;        template&lt;typename Iterator,typename CompareType=std::less&lt;typename std::iterator_traits&lt;Iterator&gt;::value_type&gt;&gt;</div>
<div class="line"><a name="l00046"></a><span class="lineno">   46</span>&#160;                    <span class="keyword">typename</span> std::iterator_traits&lt;Iterator&gt;::value_type</div>
<div class="line"><a name="l00047"></a><span class="lineno"><a class="line" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#ae742d2848ba12d8cc796668091e469aa">   47</a></span>&#160;                    <a class="code" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#ae742d2848ba12d8cc796668091e469aa">randomized_select</a>(<span class="keyword">const</span> Iterator begin,<span class="keyword">const</span> Iterator end,<span class="keyword">typename</span> std::iterator_traits&lt;Iterator&gt;::difference_type rank,CompareType compare=CompareType())</div>
<div class="line"><a name="l00048"></a><span class="lineno">   48</span>&#160;        {</div>
<div class="line"><a name="l00049"></a><span class="lineno">   49</span>&#160;            <span class="comment">//typedef typename std::iterator_traits&lt;Iterator&gt;::value_type T;</span></div>
<div class="line"><a name="l00050"></a><span class="lineno">   50</span>&#160;            <span class="keyword">auto</span> size=std::distance(begin,end);</div>
<div class="line"><a name="l00051"></a><span class="lineno">   51</span>&#160;            assert(size&gt;=0);</div>
<div class="line"><a name="l00052"></a><span class="lineno">   52</span>&#160;            assert(rank&lt;size);</div>
<div class="line"><a name="l00053"></a><span class="lineno">   53</span>&#160;            <span class="keyword">using</span> <a class="code" href="namespace_introduction_to_algorithm_1_1_sort_algorithm.html#a3a2d13a83cd168d9a10df0ed8c39f9ee">IntroductionToAlgorithm::SortAlgorithm::partition</a>;</div>
<div class="line"><a name="l00054"></a><span class="lineno">   54</span>&#160;            <span class="keyword">auto</span> partitioned_iter=<a class="code" href="namespace_introduction_to_algorithm_1_1_sort_algorithm.html#a3a2d13a83cd168d9a10df0ed8c39f9ee">partition</a>(begin,end,begin+<a class="code" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#a117ee8d5d70d91c5be1d412f9fbad1cd">radom_index</a>(0,size-1),compare); <span class="comment">//随机划分</span></div>
<div class="line"><a name="l00055"></a><span class="lineno">   55</span>&#160;            <span class="keyword">auto</span> distance=std::distance(begin,partitioned_iter);</div>
<div class="line"><a name="l00056"></a><span class="lineno">   56</span>&#160;            <span class="keywordflow">if</span>(distance== rank)  <span class="comment">//找到了该排位的数</span></div>
<div class="line"><a name="l00057"></a><span class="lineno">   57</span>&#160;                <span class="keywordflow">return</span> *partitioned_iter;</div>
<div class="line"><a name="l00058"></a><span class="lineno">   58</span>&#160;            <span class="keywordflow">else</span> <span class="keywordflow">if</span>(distance&lt;rank) <span class="comment">//已知某排位的数位次较低，则指定排位数的元素在它右侧</span></div>
<div class="line"><a name="l00059"></a><span class="lineno">   59</span>&#160;                <span class="keywordflow">return</span> <a class="code" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#ae742d2848ba12d8cc796668091e469aa">randomized_select</a>(partitioned_iter+1,end,rank-distance-1,compare); <span class="comment">//从partitioned_iter+1，则找右侧的第rank-distance-1位</span></div>
<div class="line"><a name="l00060"></a><span class="lineno">   60</span>&#160;            <span class="keywordflow">else</span>                   <span class="comment">//已知某排位的数位次较高，则指定排位数的元素在它左侧</span></div>
<div class="line"><a name="l00061"></a><span class="lineno">   61</span>&#160;                <span class="keywordflow">return</span> <a class="code" href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#ae742d2848ba12d8cc796668091e469aa">randomized_select</a>(begin,partitioned_iter,rank,compare);</div>
<div class="line"><a name="l00062"></a><span class="lineno">   62</span>&#160;        }</div>
<div class="line"><a name="l00063"></a><span class="lineno">   63</span>&#160;    }</div>
<div class="line"><a name="l00064"></a><span class="lineno">   64</span>&#160;}</div>
<div class="line"><a name="l00065"></a><span class="lineno">   65</span>&#160;</div>
<div class="line"><a name="l00066"></a><span class="lineno">   66</span>&#160;<span class="preprocessor">#endif // RANDOMIZED_SELECT</span></div>
<div class="line"><a name="l00067"></a><span class="lineno">   67</span>&#160;</div>
<div class="ttc" id="namespace_introduction_to_algorithm_1_1_select_algorithm_html_a117ee8d5d70d91c5be1d412f9fbad1cd"><div class="ttname"><a href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#a117ee8d5d70d91c5be1d412f9fbad1cd">IntroductionToAlgorithm::SelectAlgorithm::radom_index</a></div><div class="ttdeci">IntType radom_index(IntType begin, IntType end)</div><div class="ttdoc">radom_index： 生成随机整数 </div><div class="ttdef"><b>Definition:</b> <a href="randomizedselect_8h_source.html#l00018">randomizedselect.h:18</a></div></div>
<div class="ttc" id="namespace_introduction_to_algorithm_1_1_select_algorithm_html_ae742d2848ba12d8cc796668091e469aa"><div class="ttname"><a href="namespace_introduction_to_algorithm_1_1_select_algorithm.html#ae742d2848ba12d8cc796668091e469aa">IntroductionToAlgorithm::SelectAlgorithm::randomized_select</a></div><div class="ttdeci">std::iterator_traits&lt; Iterator &gt;::value_type randomized_select(const Iterator begin, const Iterator end, typename std::iterator_traits&lt; Iterator &gt;::difference_type rank, CompareType compare=CompareType())</div><div class="ttdoc">randomized_select： 算法导论第9章9.2 顺序统计量的随机选择算法 </div><div class="ttdef"><b>Definition:</b> <a href="randomizedselect_8h_source.html#l00047">randomizedselect.h:47</a></div></div>
<div class="ttc" id="quicksort_8h_html"><div class="ttname"><a href="quicksort_8h.html">quicksort.h</a></div></div>
<div class="ttc" id="namespace_introduction_to_algorithm_1_1_sort_algorithm_html_a3a2d13a83cd168d9a10df0ed8c39f9ee"><div class="ttname"><a href="namespace_introduction_to_algorithm_1_1_sort_algorithm.html#a3a2d13a83cd168d9a10df0ed8c39f9ee">IntroductionToAlgorithm::SortAlgorithm::partition</a></div><div class="ttdeci">Iterator partition(const Iterator begin, const Iterator end, const Iterator partition_iter, CompareType compare=CompareType())</div><div class="ttdoc">partition： 算法导论第7章快速排序中的划分算法 </div><div class="ttdef"><b>Definition:</b> <a href="quicksort_8h_source.html#l00043">quicksort.h:43</a></div></div>
<div class="ttc" id="namespace_introduction_to_algorithm_html"><div class="ttname"><a href="namespace_introduction_to_algorithm.html">IntroductionToAlgorithm</a></div><div class="ttdoc">Namespace of IntrodunctionToAlgorithm. </div><div class="ttdef"><b>Definition:</b> <a href="longest__common__subsequence_8h_source.html#l00024">longest_common_subsequence.h:24</a></div></div>
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